The Time Division Duplex (TDD) mode which is one of two general duplex systems refers to the use of the same operating band in the uplink and the downlink, transmission of uplink and downlink signals over different time intervals and the presence of a Guard Period (GP) between the uplink and the downlink.
There is a frame structure of a Long Term Evolution (LTE) TDD system as illustrated in FIG. 1, where a radio frame has a length of 10 ms and includes two types of sub-frames which are special sub-frames and normal sub-frames, totaling to 10 sub-frames, each of which is 1 ms. The special sub-frames include three sub-frames which are a Downlink Pilot Slot (DwPTS) for transmission of a Primary Synchronization Signal (PSS), a Physical Downlink Control Channel (PDCCH), a Physical Hybrid Automatic Repeat Request (HARQ) Indication Channel (PHICH), a Physical Control Format Indication Channel (PCFICH), a Physical Downlink Shared Channel (PDSCH), etc.; a GP for a guard period between the downlink and the uplink; and an Uplink Pilot Slot (UpPTS) for transmission of a Sounding Reference Signal (SRS), a Physical Random Access Channel (PRACH), etc. The normal sub-frames include uplink sub-frames and downlink sub-frames for transmission of an uplink/downlink control channel, service data, etc. The sub-frame 0 and the sub-frame 5 as well as the DwPTS sub-frame among the special sub-frames are constantly used for downlink transmission, the sub-frame 2 and the UpPTS sub-frame among the special sub-frames are constantly used for uplink transmission, and the other sub-frames can be configured for uplink transmission or downlink transmission as needed.
Uplink/downlink signals are transmitted in different sub-frames over the same frequency resources in the uplink and the downlink in a TDD system. In common TDD systems including a 3G Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) system and a 4G TD-LTE system, uplink and downlink sub-frames are allocated statically or semi-statically, and a common practice is to plan a network by determining the proportion of uplink to downlink sub-frames according to the type of a cell and a rough proportion of traffic and keeping the proportion unchanged. This is a simple practice in the context of large coverage by a macro cell. However an increasing number of low-power base stations including a pico cell, a home NodeB, etc., have been deployed for small local coverage along with the advancement of technologies, and there are a small number of users and a significantly varying demand of the users for traffic in these cells, thus resulting in a dynamically varying proportion of uplink to downlink traffic as needed in the cells.
In order to address this problem, there has been proposed a scheme for dynamic allocation of uplink and downlink sub-frames, where four types of sub-frames are set in a specific period of time (for example, which is a radio frame) respectively as sub-frames constantly used for downlink transmission, sub-frames constantly used for uplink transmission, special sub-frames and flexible sub-frames allocated flexibly for uplink or downlink transmission, and the uplink and downlink configuration of the sub-frames can be varied dynamically due to the flexible sub-frames in the radio frame to thereby accommodate a demand for traffic in the cell. However there has been absent so far an uplink and downlink Hybrid Automatic Repeat reQuest (HARQ) timing relationship for the scheme for dynamic allocation of uplink and downlink sub-frames.
In summary there has been absent so far an uplink and downlink HARQ timing relationship for the scheme for dynamic allocation of uplink and downlink sub-frames.